The present invention relates to a method of casting a product.
It is often not necessary for the whole of a cast product to have a function that is required for only a part of the product. For example, an abrasive face of the cylinder portion in an engine block requires high wear resistance; however, the wear resistance is not required for the other portions. Therefore, it is sufficient in the cast product that only the necessary portion or the surface has the required function.
In such a case it has been conventionally proposed as a method of adding the wear resistance to a portion of a cast product, for example, to set a preform comprising alumina, silicon nitride, silicon carbide or whiskers of these in a fiber form in a mold cavity and to force a molten metal into the mould cavity and into gaps among respective fibers. However, according to this method much restriction is imposed on the shape of the product, manufacturing steps are prolonged and the machinability of the product as cast is poor, giving rise to a disadvantage of very high production cost.
Hence, the applicants have previously proposed a method of providing a wear resistant layer on the surface of a cast product by directly casting metal together with wear resistant fine particles as disclosed in Japanese Unexamined Patent Publication No. Hei 7-124739. However, according to this conventional method, when the size of the wear resistant fine particles is increased, the machinability is deteriorated. On the other hand, when the size of the wear resistant fine particles is decreased, the thickness of the wear resistant layer becomes very thin. Moreover, when the metal is cast together with the wear resistant fine particles, there is a risk that the function of the cast product will not be achieved since a binder holding the wear resistant fine particles remains in the cast product and it is difficult to increase the thickness of the wear resistant layer.
In Patent Abstracts of Japan vol. 095, No 008.29 September 1995 and JP 07 124739A, it is set forth that a collapsible core can be provided with a coating before a casting step, and the coating remains with the casting after the core is collapsed and removed, but this publication does not disclose the nature of the coating, and so it does not deal with the objective of the present invention.
Also, in U.S. Pat. No. 3,945,423 (E1) the inventor is concerned with the formation of a wear resistant shell by electro-deposition of a layer on the surface of a core, so that at the end of forming of the layer, the electric current is increased, which has the effect of making the deposited layer surface rough. The core with the rough surface is placed in a bath of coating metal material (eg aluminium) which binds mechanically by virtue of the rough surface of the deposited layer, and then the core with the layer and aluminium coating is placed in a mould for the formation of the cast product. Eventually, the core is removed, and the cast product has a hard surface characteristic. The disclosure is not concerned with coating wear resistant particles with aluminium or the like, but rather that a layer of aluminium is placed on an electro-deposited layer, which probably is not made up of granules or particles.
In Patent Abstracts of Japan vol. 018, No 538 (M-1686), Oct. 13, 1994 and JP 06 190537A it is disclosed that a wear resistant surface is provided on a cast product, by mixing metal powder and xe2x80x9cwafer glass basexe2x80x9d to form xe2x80x9craste-statexe2x80x9d. The resulting mixture is coated on the part of the mould where the wear resistant surface is to be formed on the cast product. After the material is so coated, the molten material is cast into the mould. The result is a xe2x80x9creformed layer on the surface of the castingxe2x80x9d.
There is no disclosure of the specific extent of coating of the wafer glass base.
In Patent Abstracts of Japan vol. 014 323 (M-0997) Jul. 11, 1990 and No JP 02 108447A it is set forth that a mould core is first of all coated with a mixture of xe2x80x9cwafer glass series inorganic binderxe2x80x9d and zircon powder. Other coatings are added. When the core has been finally coated, it is fixed in the die and the casting metal material is cast around the core. The core is eventually removed, and the resulting product has a surface characteristic which it would not otherwise have without the surface coating. There is no disclosure of the extent of coating, if any, of function selecting material.
It is a first object of the present invention to provide a method of casting a product with a surface having a required function such as wear resistance that is formed easily and inexpensively by means of a normally known pressure casting process.
Further, it is a second object of the present invention to provide a method of casting a product with a function selecting layer of sufficient thickness formed on the surface even when very fine function selecting materials are used, and wherein the machinability of the product as cast is excellent.
According to the invention there is provided a method of casting a product by inserting casting material into a mould cavity, and by which method the product is provided on at least a part of its surface with a layer of intermediate material comprising a function selecting material which has at least one physical property which is different from that of the casting material, and a coating material which is the same as or is from the same group as the casting metal material, and wherein the layer is located in the casting mould cavity prior to inserting the casting metal material into the casting mould cavity and wherein the intermediate material is formed by coating at least half of the function selecting material with the coating material.
Preferably, the function selecting material comprises particles and in one example the function selecting material comprises two different types of function selecting particles.
It is preferred that the intermediate material is granular in nature, and that the layer is provided by a perform of the intermediate material.
In a specific example, the intermediate material comprises at least two types of granular intermediate materials, each of which is formed by coating at least half the surface with the coating metal material.
In another example, the intermediate material is mixed with another function selecting material of at least one physical property which is different from that of the function selecting material of the intermediate material.
When the intermediate material is granular in nature, the granules of the intermediate material preferably have a size in the range 50 xcexcm to 100 xcexcm.
According to a specific method, the intermediate material is formed by depositing atomized droplets of a molten metal composition which comprises the function selecting material and the coating metal material onto a collector.
In another specific method, the intermediate material is formed by depositing atomized droplets of a molten metal composition which comprises the function selecting material and the coating metal material onto a collector and the atomized droplets form a semi-molten film in which the solid phase to liquid phase ratio is about 80% and on which surface the solid phase to liquid phase is less than 80%.
Preferably, to locate the intermediate material in the casting mould cavity, the intermediate material is mixed with adhesive and formed as a preset core, which is subsequently located in position in the mould cavity.
Alternatively, to locate the intermediate material in the casting mould cavity, the intermediate material is adhered by adhesive to a surface of a preset core, which is located in position in the mould cavity.
Again, to locate the intermediate material in the casting mould cavity, the intermediate material is adhered in position to the mould cavity by using adhesive to adhere the intermediate material to the surface of the mould cavity.
In any of these cases the adhesive comprises one or more selected from the group consisting of phenolic resin, fran resin, unsaturated polyester resin, urethane resin, polyvinyl acetate resin, polyvinyl chloride resin, inorganic cement, sodium silicate and low melting point metals.
The coating metal material comprises one selected from the group consisting of aluminium, magnesium, zinc, copper, iron and alloys thereof and the function selecting material may comprise one or more selected from the group comprising a primary crystal silicon particle crystallised to a hyper-eutectic Alxe2x80x94Si alloy powder, a carbon particle precipitated to a cast iron powder, SiC, Al2O3, Si3N4, SiO2, TiC, graphite, lead, molybdenum disulfide, iron, intermetallic compounds precipitated to aluminium series alloys, K2Oxe2x80x946TiO2, nickel alloys, cobalt alloys, ferrite magnet, magnetic steels, cobalt, pumice, shirasu balloon, alumina balloon, carbon balloon and hollow glass beads.